Last March, when President Obama swept into Israel determined to patch up the fraught relationship with Prime Minister Benjamin Netanyahu, the labored effort on both sides was so obvious as to be a bit painful. Israeli television carried every public moment of the visit live, including a midday tour Netanyahu gave Obama of new Israeli inventions. The highlight was the Rewalk technology, a kind of exoskeleton that allows a person who would otherwise be confined to a wheelchair to stand up and walk around.

“Well, we gotta get a picture of this,” the visiting American said, and snugged in with Netanyahu beside a gadget that, on top of everything else, captured the essence of their new relationship: awkward and far from natural, yes, but, hey, whatever works.

But eight months later, as talks resume Wednesday in Geneva on the fate of the Iranian nuclear program, Obama and Netanyahu once again are no longer talking eye to eye. Both leaders obviously want to prevent Iran from developing the atomic weapons that Tehran insists it does not even want. But a public rift has opened over the most effective route to blocking the perceived threat. And while Israel has no seat at the Geneva talks, the Jewish state plays a significant role in how they are perceived — especially on Capitol Hill, where already Obama faces so much hawkish skepticism he had to ask lawmakers to hold off on adding additional sanctions to let the talks run their course.

The rift with Israel could come to a head this week, if negotiators complete an agreement that Washington says will only be temporary and Netanyahu warns will become permanent.

It comes down to perspective. All agree that Iran has the basic ingredients of a nuclear weapon. There’s also consensus that Tehran would need very little time — perhaps as little as a month — to assemble one, if it chose to do so. American negotiators say that’s exactly what drives the urgency for an interim agreement — a pact that obliges Iran to cease the most crucial work for the six months the parties say they need to make a more comprehensive bargain. The final pact may well demand more of Iran, but for now, “We need to put some time back on the clock,” a senior administration official said in advance of the first round in October.

Netanyahu says a single, comprehensive deal is the only way forward. He says Washington is dangerously naive — his warm embrace over the weekend of visiting French President François Hollande (“French kissing in the Knesset” ran one headline) was thanks to Paris stiffing up the terms in the last round of talks — and warns that Iran is not to be trusted to honor an interim pact. Look at what happened the last time a temporary deal was attempted, he says: the 2005 temporary halt of its nuclear program ended with Tehran simply resuming a project that had grown more technically advanced and robust while talks with European diplomats droned on without result.

If that happens again, Israel will once again face the question of whether to launch a military strike, notes Michael Herzog, a retired Israeli brigadier who served as chief of staff to Ehud Barak when he was Defense Minister, in Netanyahu’s last term. Barak and Netanyahu together drove the Iranian nuclear issue to the top of the global agenda, not least by repeatedly threatening to launch air strikes against Tehran. “I believe Israel will once again face a decision point whether or not to apply a military option,” Herzog says, adding: “I don’t believe they’re bluffing.”

The gravity of that looming decisions accounts for the sharp, even combative tone used by Israeli leaders during the Geneva talks, Herzog says. “It’s why I believe they react so strongly before the deal is made, in order to avert what they fear will be a bad deal.”

Netanyahu and his ministers also warn that the West’s price of the interim agreement — the release of several billion dollars long frozen by Washington — will shatter enforcement of the economic sanctions that brought Iran to the bargaining table. One Netanyahu loyalist, Intelligence Minister Yuval Steinitz, insists the immediate sanctions relief will reach into the tens of billions, figures denied by U.S. officials.

Worst of all, Israeli officials warn, the temporary pact would leave Iran as a “threshold” nuclear power, granting international legitimacy to a nuclear program that retains the capability to sprint to creation of a nuclear weapon. “Nobody is concerned about the Japanese or British nuclear capabilities,” Steinitz said last week. “It’s totally different with Iran. If Iran will remain a threshold country, other countries in its vicinity will try to follow.”

For its part, Iran is girding for a throwdown on the crucial question of whether it has the “right” to enrich uranium. In a YouTube video released Tuesday, Iranian Foreign Minister Mohammad Javad Zarif solemnly frames the matter as one of “pride” and “integrity.” Some Iranians dryly noted that they couldn’t see what Zarif called “Iran’s message” because their government continues to block YouTube, as well as Facebook and other social media.

Karl Vick has been TIME's Jerusalem bureau chief since 2010, covering Israel,the Palestine territories and nearby sovereignties. He worked 16 years at the Washington Post in Nairobi, Istanbul, Baghdad, Los Angeles and Rockville, MD.